<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    body{
      margin: 0;
      padding: 0;
      background-image: url(../images/grid.png);
    }
    canvas{
      background-color: rgba(255, 0, 0, 0.1);
    }
  </style>
</head>
<body>

  <canvas id="tutorial" width="300" height="300px">
    你的浏览器不兼容Canvas,请升级您的浏览器!
  </canvas>

  <script>
    window.onload = function() {
      let canvasEl = document.getElementById('tutorial')
      if(!canvasEl.getContext){
        return
      }
      let ctx = canvasEl.getContext('2d') // 2d | webgl
      
      // 2.修改画笔的颜色
      ctx.fillStyle = 'rgba(255, 0, 0, 0.3)'
      ctx.fillRect(0,0, 100, 50) // 单位也是不用写 px

      ctx.strokeStyle = 'blue'
      ctx.strokeRect(200, 0, 100, 50)

      ctx.strokeStyle = 'green' // 关键字, 十六进制, rbg , rgba
      ctx.beginPath()
      ctx.rect(0, 100, 100, 50)
      ctx.stroke()

    }
  </script>
</body>
</html>